This invention relates to the use of poly(arylene ether) polymers, and more particularly to the use of grafted functional groups onto the backbone of poly(arylene ether) polymers, to provide cross-linkable polymers with a range of glass transition temperatures and low moisture uptake having particular utility as gate dielectric layers in multilayer electronic devices such as thin film transistors. The invention also relates to methods for applying the polymers in order to form thin film transistors (TFT).
The electronics industry is seeking gate dielectric materials for use in fabricating multilayer electronic devices such as thin film transistors at low temperatures, particularly for printed transistors. However, the need for materials compatibility, processability, and good electrical properties over a wide range of conditions and deposition techniques and temperatures has presented a significant problem. This problem has been a very difficult one to solve for polymers since the desired temperature for their use in flexible or lightweight transistors (i.e. cure) is below 400° C. and more preferably below about 180° C.
Therefore, there is a need in the multilayer electronic device fabrication industry for the replacement of silicon nitride-based gate dielectric materials with materials of lower processing temperatures that may be deposited via solution casting techniques such as spin-coating, slot extrusion, or printing. Silicon nitride and its modified versions are typically processed at temperatures greater than 300° C. and are typically deposited via chemical vapor deposition techniques. While polymeric materials have been discussed as replacements for silica as interlayer dielectrics (ILDs), shallow trench isolation (STI) materials, or stop layer dielectrics (SLDs), they have not traditionally been reported to be used as gate dielectrics due to their lack of hydrophobicity or their inability to crosslink at low temperatures. In particular, polymeric systems such as the ones of the invention described below have not been employed as gate dielectrics that are resistant to solvents, that may be printed or slot extruded, are processable at or below 180 C., and give electrical properties needed in a gate dielectric. Many of the polymers that have been tested as gate dielectric materials for thin film transistors lack the hydrophobicity need to avoid moisture absorption and the ability to withstand contact with other solvents that may be used in depositing subsequent layers and that may damage the gate dielectric layer. Thus, a gate dielectric material that meets that criteria above combined with the cross-linking needed to give good solvent resistance is desirable.
Past attempts to crosslink poly(arylene ethers) utilized various high temperature crosslinking groups to give high Tg polymer and this chemistry may be used as an intra- or interlayer dielectric material for amorphous silicon or low temperature poly-silicon thin film transistors. A detailed summary of these chemistries is provided in U.S. Pat. No. 6,060,170; hereby incorporated by reference This patent teaches using poly(arylene ether) polymer compositions having aromatic groups grafted on the poly(arylene ether) backbone, which grafts allow for crosslinking of the polymers in a temperature range of 200 to 450° C. A further reduction in crosslinking temperature would, however, be desirable for dielectric and passivation materials for thin film transistors on flexible substrates or organic thin film transistors.
Display and imaging backplane or thin film transistor manufacturing require suitable coatings, especially gate dielectric insulating layers. These layers can have low or high dielectric constants and are required to have low leakage current values, good solvent resistance, and low moisture absorption. In addition, it is desired to provide the solutions that form these layers with unlimited storage stability at 25° C., storage stability at 40° C. sufficient to weather transportation in non-refrigerated vehicles, and cure temperatures of 130 to 180° C. or below 300° C. After cure, it is desirable to have solvent resistance, a dielectric constant below 3.5, and low moisture absorption.
All references cited herein are incorporated herein by reference in their entireties.